At present, control devices for various kinds of hydraulic apparatuses have been developed, for example, Chinese Utility Models No. CN 2061169 U, entitled "A hydraulic jack with automatic speed-regulation", issued on Aug. 29, 1992; No. 2101038U, entitled "A double pump oil jack", issued on Apr. 8, 1992; No. CN2107454U, entitled "A light-load speed-up hydraulic jack", issued on Jun. 17, 1992 and No. CN 2155365Y, entitled "A hydraulic elevating gear device with speed regulation", issued on Feb. 9, 1994. Each of these prior Utility Models comprises a new structure with a set of pump, valves and oil lines added to the structure of an existing jack with a set of pump, valves and oil lines, that is, whenever a pump is added, a complete set of elements should be added to correspondingly, wherein two pumps thereof drawn a portion of oil to partially raise the lifting speed of the cylinder. Obviously, they are complex in structure and the boost speed thereof is limited during the light-load. It is difficult to reduce efficiently the wear of the elements of the device, and the cylinder needs to be restored its original position by an external force. In addition, the operating processes of the devices are complicated, disadvantageously affecting fluid channel properties and system efficiency. Take the device disclosed in Utility Model No. CN2107454U for example, during heavy-load lifting process, the large-diameter plunger piston pump may cause plenty of the reactive fluid oil to flow back to the fluid reservoir, resulting in energy loss. besides, since the large pump in the prior art references is not used also as a fluid reservoir, it needs to provide a fluid reservoir to ensure fluid supply, Thus, giving rise to a series of problems, such as heavy weight and large volume, etc.
In addition, the Chinese Utility Model No. CN 2172760Y, entitled "A hand-operated double-speed vertical hydraulic jack", issued on Jul. 27, 1994, discloses a double speed hydraulic jack having a large and a small cylinders in which the inner barrel and the large piston rod are encased as an integral unit in a sleeve. The defects in the structure are as follows: A) it is suitable only large tonnage jacks having load capacity of over 32 tons, so its scope of application is narrow; B) it is inferior in reliability because the check valve a is connected with the hydraulic-controlling check valve c in parallel; C) the control is complicated since check valve b for replenishing fluid is communicated with the main passage; D) the structures of all the control valves and a majority of fluid lines of the utility model, especially the return valve, hydraulic-controlled check valve and the like are not described in the drawing clearly, and it is difficult for the solution of the utility model to be carried out.